Hello! I am from De La Salle Primary School and this was my Prelimary Exam Paper.
My teacher has said that they accepted both answers (2) and (4).
If I am not wrong, they accepted (4) as in the degree of 10 , the glass tube will contract,
thus pushing the red ink towards flask X. In a period of time , the heat in flask X will enter the
glass tube, and since heat travels upwards , it will move alone the glass tube, pushing the red
ink too.
I think this is the explanation
My answer is also (2) in the examintion and it is also accepted.
Wish you all the best in your PSLE!